Insights into the evolution of the Hindu Kush–Kohistan–Karakoram from modern river sand detrital geo- and thermochronological studies

Abstract

The Hindu Kush–Kohistan–Karakoram region is critical to understanding the long-term accretion history of the south Asian margin pre- and post-India–Asia collision and the impact of these collisions on the development of high topography. However, knowledge about this region remains incomplete owing to sparse studies. Here, we present a study comprising detrital zircon U–Pb geochronology, detrital muscovite 40 Ar/ 39 Ar thermochronology and numerical modelling on 40 Ar/ 39 Ar dates. The study identifies zircon U–Pb age peaks at 200, 110–130, 60–80 and 28–40 Ma, supporting the polyphase collisions and crustal growth in the south Asian margin. The modelling study reveals fast cooling–erosion at 115–129, 69–71, 27–35 and <8 Ma, synchronous with collision-related crustal growth, indicating the significant impact of accretion both prior to and post-India–Asia collision. This study, along with studies in eastern Karakoram, reveals along-strike variations in erosion and exhumation with young (since late Miocene) intense erosion focusing on the east–central Karakoram. We suggest that this east–west spatial variation in exhumation may have been associated with more intense crustal shortening, and thus the greater crustal thickness, topographic relief and altitude observed in the eastern compared with the western Karakoram. Supplementary material: Detrital zircon U–Pb ages, detrital muscovite single-crystal 40 Ar/ 39 Ar ages and modelling results are available at: https://doi.org/10.6084/m9.figshare.c.4124573